1. Field of the Invention
The present invention relates to a novel thermosetting resin as well as to fiber reinforced plastics made from such thermosetting resin as the matrix, which are excellent in the heat resistance, impact resistance and flexibility and also have high toughness.
2. Description of the Prior Art
Resins based on polyimide exhibit, in general, superior physical and chemical properties, such as, high heat resistance and high stability against chemicals etc., so that they have many uses, such as, films, coatings on electric cables and wires, plyed or laminated boards and sheets, paints, adhesives, and formed articles for industrial and domestic uses at higher temperatures. Among the resins based on polyimide, aromatic polyimide resins and polyamide-imide resins are both superior in the mechanical properties and heat resistance, while they have some deficiency processibility, so that their applications had been limited only to films and insulator coatings for electric wires. Employment of these resins for molding shaped articles and for manufacturing laminated boards (multilayered boards) had been limited only to a quite specific case, because conventional processing apparatuses generally employed for phenol resins, epoxy resins and so on, cannot be used, as such, due to the necessity of high temperature and high pressure for processing these polyimide resins and, thus, these latter resins require an installation specifically designed therefor.
On the other hand, resins based on aromatic bismaleimide, which also are thermosetting in nature, have widely been employed in industry, since they exhibit superior heat resistance and excellent moldability. Thermosetting resins based on aromatic bismaleimide have the defects of inferior impact resistance and poor flexibility.
In order to improve the low impact resistance and the poor flexibility of aromatic bismaleimide resins, an attempt had been proposed to incorporate an aromatic diamine compound together with the aromatic bismaleimide. Thus, a resin based on polyaminobismaleimide [e.g. Kerimide (trademark), a product of the firm Rhone-Poulenc S.A.] produced from N,N'-4,4'-diphenylmethane bismaleimide and 4,4'-diaminodiphenylmethane is superior in impact resistance and in flexibility as compared with those made from an aromatic bismaleimide alone, as disclosed in the Japanese Patent Publication Nos. 23250/1971 and 5959/1977. This thermosetting resin also has been shown to be not satisfactory in its impact resistance and flexibility.
Fiber reinforced plastics made of these polyimide resins have also a disadvantage that the mechanical strength to be expected by the incorporation of reinforcement fiber may not be revealed sufficiently, since there is considerable difference between the matrix resin and the reinforcement fiber in thermal expansion, especially when carbon fiber or aramid fiber is employed for the reinforcment, thus causing formation of microcracks in the final molded articles at around the interface between the fiber and the matrix resin due to the shrinkages and expansions that are encountered during the course of polymerization of the resin and processing works in and out of the mold involving considerable temperature changes by heating and cooling.